1. Field of the Invention
The present invention relates to a data processing apparatus and method for applying an error correction process to data read from an information storage medium such as a digital versatile disk (DVD) and, more particularly, to a data processing apparatus and method for making syndrome calculations.
2. Description of the Related Art
In recent years, DVDs that record digital data have prevailed remarkably. On a DVD, sector data generated from error correction code blocks is recorded.
Each error correction code block is made up of a block of information symbols arranged in the row and column directions, inner-code PI parity which is appended to information symbols in the row direction contained in the information symbol block, and outer-code PO parity which is appended to both information symbols in the column direction contained in the information symbol block and the inner-code PI parity.
An error correction code in the PO direction has a code length of 208 bytes, an information length of 192 bytes, and a minimum distance of 17. An error correction code in the PI direction has a code length of 182 bytes, an information length of 172 bytes, and a minimum distance of 11.
Sector data generated from such error correction code block contains an error correction code, and can undergo error correction using this error correction code. Such a technique is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-74861.
Also, Jpn. Pat. Appln. KOKAI Publication No. 2001-67822 discloses a technique associated with an error correction process that can cope with the playback speed in a high multiple-speed mode. That is, this reference discloses a technique for calculating a syndrome for data with a code length of 182 bytes in the PI direction contained in playback information in parallel with a process for temporarily storing the playback information read out from a DVD in a buffer.
However, the method of calculating a syndrome parallel to the data write process to the buffer (disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-67822) can offer an advantage in coping with high multiple-speed playback, but poses a problem of a measure against sync abnormality in a DVD.
In fact, upon conversion into sector data, data with a code length of 182 bytes in the PI direction forms two Sync frames. One Sync frame contains a sync code (2 bytes) and 91 bytes of the code length of 182 bytes in the PI direction.
A DVD system executes a synchronization process for respective Sync frames. A sync system suffers abnormality for various reasons such as the state of the servo system of the DVD system, scratches, fingerprints, dust, and the like, and at least one Sync frame may be lost or duplicated, or the arrival order of frames may be reversed.
Such problem with of Sync frames often disturbs the calculation of an effective syndrome of a data sequence (the code length of 182 bytes in the PI direction). Even if 91 bytes of one Sync frame are correct data, all 182 bytes of both the Sync frames may be consequently determined as error data. Such a burst error results in an error correction performance drop and causes correction errors.